Paper-sizing agents containing aqueous, solvent-free dispersions of cationic polymers and method of preparing sized paper by using these agents

ABSTRACT

The present invention relates to agents for the pulp and/or surface sizing of paper, which comprise aqueous, solventless dispersions of cationic polymers, and to a process for sizing paper by using said agent. The sizing agents according to the present invention which can be used both in pulp and surface sizing obtain as active substance copolymers of 
     a) 30-70 mole-% of a monomer I 
     with 
     b) 70-30 mole-% of a monomer II, 
     and optionally 
     c) 0-20 mole-% of C 8  -C 30  monoolefins, 
     and 
     d) 0-10 mole-% of further monomers copolymerizable with a), b), and optionally c), the sum of monomers a), b), c), and d) amounting to 100 mole-%.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to agents for the pulp and/or surfacesizing of paper, which comprise aqueous, solventless dispersions ofcationic polymers. The present invention further relates to a processfor sizing paper by using said agents.

2. Discussion of the Background

In the production of ink resistant and printing papers the papers aresized at the surface or in the pulp; this is to decrease the wettabilityof cellulose and the absorption of water or aqueous liquids through thecapillary system of the sheet, and to improve the absorption of printinginks, the whiteness and opacity as well as the mechanical properties ofthe paper sheet. The known sizing process and the agents normally usedare described in Ullmanns encyclopedia, volume 17 (1979), pages 585-587and 599.

It is also known to use cationic polymers in the sizing process, theystand out for a high substantivity towards cellulose fibers. JapanesePatent No. J 04 108 196 describes cationic sizing agents based oncolophony and cationic polymers. Japanese Patent Nos. J 04 091 290, J 63270 893, and J 59 159 198 describe sizing agents formed of dimericalkylketenes and cationic polymers.

DE 37 37 615 C2 describes sizing agents representing resins modifiedwith carboxylic acid, so-called fortified resins which are dispersed byportions of cationic copolymers. In this connection the cationiccopolymers are obtained by polymerization in solution, and theproduction of the dispersed sizing agent from the anionically modifiedresins and the cationic copolymers is effected in a complicated methodby removing the solvent from the copolymer by means of distillation,melting the modified resin, and dispersing in water, in some cases usingsurfactants. During application, the resin components not bound in thepulp load the process water and must be removed, if necessary by usingadditional auxiliaries.

DE 38 26 825 C2 describes cationic sizing agents that are formed frommethyl (meth)acrylate, butyl (meth)acrylate, acrylic acid, and 10-30percent by weight of portions of N,N-dimethylaminoethyl(meth)acrylate,and which comprise isopropanol or other organic solvents. The describedsizing agents are unstable during storage and insufficiently active whenapplied.

EP 416 427 B1 describes sizing agents based on aqueous, cationic polymerdispersions whose polymer portion is formed of only 2-20%-wt. of asalt-forming, water-soluble monomer having groups of alkyl ammonium,alkyl sulfonium, or alkyl phosphonium, but which are always used withadditional cationic polymers, such as retention agents and protectivecolloids (Poly-DADMAC). For this reason these polymers must neverthelessbe used in larger amounts. Additionally, the described dispersions alsocomprise emulsifiers and, in particular, nonionic surfactants which--inaddition to the water-soluble retention agents in the paper--may impairthe sizing action and load the industrial process water.

SUMMARY OF THE INVENTION

Accordingly, it was the object of the present invention to improve theknown cationic sizing agents by avoiding their disadvantages; inparticular, to provide sizing agents that can be manufactured in a moreeconomic and ecologically beneficial manner, which are stable instorage, can exclusively be used as sizing agents without employingadditional components, and moreover have an improved action.

This object is achieved by using aqueous, solvent-free dispersions ofcationic polymers as sizing agents, wherein the cationic polymers areobtained by radical polymerization in solution or dispersion, preferablyin mass, of

a) 30-70 mole-% of at least one monomer of the general formula

    H.sub.2 C═CR.sup.1 --CO--X--R.sup.2 --N(R.sup.3).sub.2 (I)

wherein R¹ =H, CH₃,

R² =a C₂ -C₄ -alkylene group,

R³ =H, a C₁ -C₄ -alkyl group, and

X=O, NH

with

b) 70-30 mole-% of at least one monomer of the formula

    H.sub.2 C═CR.sup.1 --CO--X--R.sup.4                    (II)

wherein R¹ and X have the meaning stated for compound I and R⁴ =a C₈-C₃₀ -alkyl group,

and optionally

c) 0-20 mole-% of at least one C₈ -C₃₀ -monoolefin,

and

d) 0-10 mole-% of at least one further monomer copolymerizable with a),b) and optionally c),

subsequent neutralization and optional quaternization of the copolymers,and dispersion in water or aqueous liquids, wherein the sum of monomersa), b), c), and d) amounts to 100 mole-%.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The monomers of group a) include acrylic and/or methacrylic derivativeswith an amine function. On the one hand, they are necessary for fixationto the cellulose fiber, and, on the other hand, their partially orcompletely neutralized form provides the dispersibility of the polymerin water. Suitable monomers includeN,N-dimethylaminoethyl(meth)acrylate,N,N-dimethylaminopropyl(meth)acrylate,N,N-dimethylaminoethyl(meth)acrylamide, andN,N-dimethylaminopropyl(meth)acrylamide. N,N-dimethylaminoethylacrylateand N,N-dimethylaminopropylacrylamide are preferably used.

The monomers of group a) are present in the copolymer in an amount of30-70 mole percent. If one remains under these limits, instabledispersions are generally obtained, whereas a portion of more than 70mole-% considerably deteriorates the sizing effect. It is preferred thata portion amounting to 40-60 mole-% of said monomers in the copolymer beused.

The monomers of group b) are hydrophobic esters or amides of acrylicand/or methacrylic acid. They mainly provide the sizing effect. Suitablemonomers are, for example, 2-ethylhexyl (meth)acrylate, n-octyl(meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, lauryl(meth)acrylate, isotridecyl (meth)acrylate, myristyl (meth)acrylate,stearyl (meth)acrylate, C₁₈₋₂₂ -(meth)acrylate, 2-ethylhexyl(meth)acrylamide, n-octyl (meth)acrylamide, isononyl (meth)acrylamide,decyl (meth)acrylamide, lauryl (meth)acrylamide, isotridecyl(meth)acrylamide, myristyl (meth)acrylamide, stearyl (meth)acrylamide,C₁₈₋₂₂ -(meth)acrylamide. The monomers are produced in known manner fromthe hydrophobic alcohols or amines and the (meth)acrylic acid orreactive derivatives thereof. Many of these monomers are commerciallyavailable. Stearyl methacrylate is preferably used from this group.

Part of the monomers of group b) can be replaced by long-chainmonoolefins. Suitable examples for this purpose include, for example,1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene,1-octadecene, 1-eicosene, and C₂₀₋₂₄ or C₃₀₊ -alpha-olefin fractions.These monomers are also commercially available. They may be used inrelation to the monomer group b) in an amount of 0.001 to 1:1.1-octadecene and C₂₀₋₂₄ -alpha-olefin mixtures are preferably used.

Optionally, up to 10 mole-% of additional alpha,beta-unsaturatedmonomers which are copolymerizable with the monomers of groups a), b),and optionally c) may be present in the polymerization recipe in orderto achieve special properties. The condition for their use is the factthat they can be processed into a homogeneous mixture with theabove-mentioned monomers, optionally at a higher temperature. Suitableexamples include, e.g., styrenes, vinyl ester, vinyl ether,(meth)acrylic acid and/or (meth)acrylamide.

The sizing agents preferably used according to the present inventioncomprise copolymers which are manufactured under rejection of organicsolvents by means of mass polymerization in a manner known per se.

The polymerization is carried out at temperatures of 20 to 200° C.,preferably 60 to 160° C. It is initiated thermally, photochemically, orredox-catalytically, preferably with the aid of peroxo and/or azocompounds. Owing to the mainly hydrophobic nature of the monomers,oil-soluble initiators are preferred, e.g.,2,2'-azobis(isobutyronitrile) (AIBN),2,2'-azobis(2-methylbutyronitrile), 4,4'-azo(4-cyanopentanoic acid),2,2'-azobis(2,4-dimethylvaleronitrile), di-tert-butyl peroxide,dibenzoyl peroxide, or tert-butylperoxy-2-ethyl hexanoate.

The number average of the copolymers' molar mass amounts to 1,000 to100,000 g/mole. The molar mass is preferably controlled by using knownregulators, such as mercaptoethanol or dodecyl mercaptan.

In additionally preferred embodiments, a part or the total amount of themonomers is prepared, the initiator--either completely or in partialamounts--added to the polymerization mixture at a suitable temperature,and the further reaction carried out under adiabatic conditions, withthe resulting heat of polymerization heating the reaction batch.

After polymerization, the copolymer is immediately neutralized withdilute acid and emulsified in water. In this connection, the amount ofacid is chosen such that a pH of 8 to 3 adjusts in the final product.Both inorganic acids, such as hydrochloric acid or sulfuric acid, andorganic acids, in particular carboxylic acids, such as formic acid oracetic acid, are suitable for neutralization purposes.

After neutralization or emulsification, initiators may be added oncemore to reduce the residual monomer content, if necessary. To this endboth oil-soluble and water-soluble initiator systems are suitable.

According to another preferred embodiment, copolymers are used the aminogroups of which are partially or completely reacted with a suitablequaternizing agent. Examples of suitable quaternizing agents includemethyl chloride, benzyl chloride, dimethyl sulfate and/orepichlorohydrin. The amount of quaternizing agent is chosen such thatthe degree of quaternization adjusts to 1-100 mole-%, preferably 5 to 50mole-%.

The solids content of the polymer dispersions to be used according tothe present invention amounts to 10-60%-wt., preferably 20-50%-wt., andmost preferably 30-40%-wt.

Most surprisingly, the copolymer dispersions to be used according to thepresent invention--despite the fact that they are produced without anyadditional auxiliary agents--stand out for a good dispersion stability;for this reason there is no separation or coagulation of polymer evenafter several weeks of storage at 50° C. In addition, and this cannot beexpected per se, they stand out for a good sizing action, making themsuitable for the water-repellent sizing of papers, in particular ofwriting and printing papers. In this connection, they may be used bothin pulp sizing and as surface sizing agents.

The present invention further relates to a process for sizing paper byusing the agents according to the present invention, that is both forpulp and surface sizing.

In pulp sizing, the polymer dispersions are added to the high-density orlow-density pulp at 0.1-3.0% of active substance (relative to abs. drypulp), whereas in surface sizing, 0.1-5.0 g of active substance per m²is applied to the paper after the drying part. In most cases, immediatesizing can be achieved with the polymer dispersions, that means thedesired water repellency of the paper is achieved immediately after theproduction process. The disadvantageous process of aging freshly sizedpapers, which is frequently necessary when currently used sizing agentsare employed in order to obtain hydrophobic effects and the resultingpaper properties, can therefore be omitted to a great extent.

In addition, the amount of cationic polymer dispersions used canexcellently adjust a graded sizing degree of the papers, which isreproducible both in the acid and the neutral or alkaline papermanufacture. Most advantageously, there is no need to use additionalauxiliary agents for the sizing.

The present invention will be illustrated in the following Examples.

General Specification for Preparation A:

The monomers and optional regulators are placed in a reactor equippedwith mechanical stirrer, reflux condenser, and internal thermometer andpurged with nitrogen gas for 30 minutes. Then heating to the intendedstarting temperature is effected. Subsequently, the initiator is added.The starting polymerization causes a temperature elevation. Afterexceeding the temperature maximum, stirring at the intendedpolymerization temperature is continued for three hours. Subsequently,dilute acid is added for neutralization, and stirring at 60-90° C.continued for another 30 minutes, if necessary, after renewed initiatoraddition. Cooling to 30-40° C. is effected under stirring, and theproduct is filled.

General Specification for Preparation B:

The solvent and optional regulators are placed in the same reactor as informula A and gassed with nitrogen. Afterwards heating to the intendedpolymerization temperature is effected; the monomers and the initiator(optionally diluted with additional solvent) are fed simultaneouslythrough different inlets over the intended reaction time. Aftertermination of the feeding, the reaction is allowed to continue for 2hours. Subsequently, the polymer is neutralized with dilute acid as isformula A and emulsified. The solvent is largely removed from theemulsion by distillation.

Manufacture of the Copolymers:

The copolymer dispersions manufactured according to the abovementionedinstructions are listed in the following Examples. The given numericaldata represent parts by weight. The abbreviations used have thefollowing meaning:

    ______________________________________    ACP           4,4'-azo(4-cyanopentanoic acid)    AIBN          2,2'-azobis(isobutyronitrile)    DIMAPA        N,N-dimethylaminopropylacrylamide    DM            dodecyl mercaptan    DMAEA         N,N-dimethylaminoethylacrylate    DMS           dimethyl sulfate    ECH           epichlorohydrin    EHMA          ethylhexyl methacrylate    HAc           acetic acid    ME            mercaptoethanol    StMA          stearyl methacrylate    dry subst.    dry substance    ______________________________________

The storage stability was rated at room temperature and at 50° C. Adispersion which does not separate during at least 7 days of storage at50° C. and during 1 month of storage at room temperature is consideredto be stable. The viscosities were each measured at room temperatureusing a Brookfield rotary viscometer.

    ______________________________________    Copolymer A:             method A, 60 DIMAPA, 100 StMA, 1.5 ME, T.sub.start             80° C., 1.0 AIBN, 1.5 h at 90-150° C., 38.0 HCl             (37%), 410 H.sub.2 O demin.,             bright, stable emulsion, dry subst. 30%, 460 mPas,             pH (10% in H.sub.2 O) 2.9    Copolymer B:             method A, 60 DIMAPA, 100 StMA, 7.5 ME, T.sub.start             80° C., 5.0 ACP, 1.5 h at 90-120° C., 35.7 HCl             (37%), 127 H.sub.2 O demin.,             bright, stable emulsion, dry subst. 50%, 900 mPas,             pH (10% in H.sub.2 O) 3.8    Copolymer C:             method A, 50 DIMAPA, 100 StMA, 1.5 ME, T.sub.start             80° C., 1.0 AIBN, 1.5 h at 90-150° C., 31.5 HCl             (37%), 265 H.sub.2 O demin., subsequent initiation using             1.0 H.sub.2 O.sub.2 (30%) and 0.1 ME             bright, stable emulsion, dry subst. 35%, 34,000             mPas, pH (10% in H.sub.2 O) 3.2    Copolymer D:             method A, 50 DIMAPA, 110 StMA, 1.5 ME, T.sub.start             80° C., 1.0 AIBN, 90 min. at 90-150° C., 31.5 HCl             (37%), 400 H.sub.2 O demin., subsequent initiation using             0.2 ABAH in 5 H.sub.2 O demin.             bright, stable emulsion, dry subst. 30%, 740 mPas,             pH (10% in H.sub.2 O) 3.1    Copolymer E:             method A, 50 DIMAPA, 110 StMA, 1.5 ME, T.sub.start             80° C., 1.0 AIBN, 2 h at 90-140° C., 31.5 HCl             (37%),             400 H.sub.2 O demin.,             bright, stable emulsion, dry subst. 30%, 1680             mPas, pH (10% in H.sub.2 O) 3.1    Copolymer F:             method A, 50 DIMAPA, 100 StMA, 1.5 ME, T.sub.start             80° C., 1.0 AIBN, 1.5 h at 90-150° C., 18.8 HAc,             500             H.sub.2 O demin.,             aftertreatment with 14.8 ECH, 5 h 30° C             bright, stable emulsion, dry subst. 26%, 150 mPas,             pH (10% in H.sub.2 O) 5.7    Copolymer G:             like Copolymer F, however, aftertreatment with             1.48 ECH, 5 h 80° C., bright, stable emulsion, dry             subst. 26%, 280 mPas, pH (10% in H.sub.2 O) 5.2    Copolymer H:             like Copolymer F, however, aftertreatment with             20.2 DMS, 5 h 80° C., bright, stable emulsion, dry             subst. 26%, 120 mPas, pH (10% in H.sub.2 O) 4.4    Copolymer I:             method B, 100 isopropanol, 1.5 ME, 50 DIMAPA,             100 StMA, 2.0 ACP in 20 isopropanol, addition for             1 h at 75-80° C., 5 h 90° C., 30.0 HCl (37%), 250             H.sub.2 O demin. 1 h at 80° C.,             subsequent removal of isopropanol by distillation             bright, stable emulsion, dry subst. 35%, 250 mPas,             pH (10% in H.sub.2 O) 4.3    Copolymer J:             method A, 50 DIMAPA, 95 StMA, 5 EHMA, 1.5 ME,             T.sub.start 80° C., 1.0 AIBN, 1.5 h 80-155° C.,             31.5 HCl             (37%), 265 H.sub.2 O demin., subsequent initiation using             0.2 ABAH in 5 H.sub.2 O demin., 1 h 90° C.             bright, stable emulsion, dry subst. 35%, 750 mPas,             pH (10% in H.sub.2 O) 5.9    Copolymer K:             method A, 72 DMAEA, 165 StMA, 1.5 ME, 1.0             AIBN, 1.5 h 80-135° C., 49.2 HCl (37%), 1030 H.sub.2 O             demin., subsequent initiation using 0.2 ABAH in 5             H.sub.2 O demin., 1 h 90° C.             bright, stable emulsion, dry subst. 20%, 480 mPas,             pH (10% in H.sub.2 O) 3.0    Comparative             according to Example 4 of DE 38 26 825 C2    product: white emulsion, forms layers after 3 days at room             temperature             dry subst. 16%, 30 mPas, pH (10% in H.sub.2 O)    ______________________________________             3.2

To examine the sizing action of the polymer dispersions, sheets of paperhaving a basis weight of about 100 g/m² were manufactured in a"Rapid-Kothen"-sheet former. A ground fiber cellulose (birch-sulfate) ora waste paper (newsprint paper), or a wood pulp were used as rawmaterials.

The sizing agent to be examined was added to the pulp/water-mixture andmixed for 15 seconds. Then the sheet was formed in the sheet former anddried in the vacuum drier of the Rapid-Kothen-device at 92° C. for 10minutes.

The sizing values, measured according to DIN 53132 "Water absorptionaccording to Cobb", were determined immediately after production, afteran additional drying at 110° C. for 10 minutes, and after 24 h. Theresults are listed in the following Tables.

                  TABLE 1    ______________________________________                       Cobb-value                       (g/m.sup.2)                                   after  after           Co-     Amount.sup.1)   manu-  add.  after    Example           polymer in %     Paper pulp                                   facture                                          drying                                                24 h    ______________________________________    1      A       2.0      cellulose                                   36     31    26    2      B       2.0      cellulose                                   88     28    18    3      C       2.0      cellulose                                   28     21    20    4      D       2.0      cellulose                                   53     30    28    5      E       2.0      cellulose                                   68     25    19    6      H       2.0      cellulose                                   28     25    23    7      I       2.0      cellulose                                   n.b.   61    36    8      J       2.0      cellulose                                   86     21    19    9      K       2.0      cellulose                                   n.d.   58    34    Comp.  Comp.   2.0      cellulose                                   155    54    51    Exam. 1           Prod.    ______________________________________     .sup.1) % dry subst. polymer, relative to abs. dry paper pulp

Table 1 shows that the copolymers to be used according to the presetinvention provide a very good immediate sizing. The Comparative Exampledoes not show an immediate sizing and results in considerably inferiorvalues even after 24 h, as compared to the Examples according to thepresent invention.

                  TABLE 2    ______________________________________                       Cobb-value                       (g/m.sup.2)                                 after  after    Co-        Amount.sup.1)     manu-  add.  after    polymer    in %     Paper pulp                                 facture                                        drying                                              24 h    ______________________________________    10     B       0.50     cellulose                                   --     211   49                   1.00     cellulose                                   175    34    18    11     C       0.50     cellulose                                   --     126   40                   1.00     cellulose                                   114    38    22    12     F       0.25     cellulose                                   --     110   101                   0.50     cellulose                                   91     19    19    13     G       0.50     cellulose                                   n.d.   50    43                   1.00     cellulose                                   58     24    22    14     H       1.00     cellulose                                   66     38    33    Comp.  Comp.   0.50     cellulose                                   --     169   112    Exam.2 Prod.   1.00     cellulose                                   157    75    65    ______________________________________     .sup.1) % dry subst. polymer, relative to abs. dry paper pulp

Table 2 illustrates that when the copolymers are used according to thepresent invention an advantage over known solvents can be observed evenat low concentrations.

                  TABLE 3    ______________________________________                                        Cobb-value                                        (g/m.sup.2)                                  after after           Copoly- Amount         manu- add.    after    Example           mer     in %    Paper pulp                                  facture                                        drying  24 h    ______________________________________    15     F       0.5     wood pulp                                  --    109     88                   1.0     wood pulp                                  186   37      24                   2.0     wood pulp                                  33    26      17    16     G       1.0     wood pulp                                  n.d.  69      61                   2.0     wood pulp                                  48    39      31    17     H       1.0     wood pulp                                  --    --      62                   2.0     wood pulp                                  --    44      31    ______________________________________

                  TABLE 4    ______________________________________                                        Cobb-value                                        (g/m.sup.2)                  A-              after after    Ex-   Copoly- mount.sup.1)    manu- add.    after    ample mer     in %    Paper pulp                                  facture                                        drying  24 h    ______________________________________    18    B       2.0     waste paper                                  --    171     81    19    D       2.0     waste paper                                  --    172     95    20    F       0.5     waste paper                                  --    142     141                  1.0     waste paper                                  --    54      38                  2.0     waste paper                                   89   23      18    21    G       2.0     waste paper                                  112   48      42    Comp. Comp.   1.0     waste paper                                  --    166     157    Exam. 3          Prod.   2.0     waste paper                                  --    116     109    ______________________________________     .sup.1) % dry subst. polymer, relative to abs. dry paper pulp

The results shown in Table 4 demonstrate that according to the presentinvention, as compared to the Comparative Product, a considerablyimproved immediate sizing--which is further improved after 24 h ofstorage--is achieved even in case of waste paper which can only hardlybe rendered hydrophobic.

We claim:
 1. Paper sizing agents comprising cationic, aqueous,solvent-free dispersions of cationic polymers, characterized by acontent of cationic polymers which are obtained by radicalpolymerization in solution or dispersion or in bulk ofa) 30-70 mole-% ofat least one monomer of the general formula

    H.sub.2 C═CR.sup.1 --CO--X--R.sup.2 --N(R.sup.3).sub.2 (I)

wherein R¹ =H, CH₃,R² =a C₂ -C₄ -alkylene group, R³ =H, a C₁ -C₄ -alkylgroup, and X=O, NHwith b) 70-30 mole-% of at least one monomer of theformula

    H.sub.2 C═CR.sup.1 --CO--X--R.sup.4                    (II)

wherein R¹ and X have the meaning stated for compound (I) and R⁴ =a C₈-C₃₀ -alkyl group,and c) 0-20 mole-% of at least one C₈ -C₃₀-monoolefin,and d) 0-10 mole-% of at least one further monomercopolymerizable with a), b) and c),subsequent neutralization andoptional quaternization of the copolymers, and dispersion in water oraqueous liquids, wherein the sum of monomers a), b), c), and d) amountsto 100 mole-%.
 2. The paper sizing agents according to claim 1characterized in that the aqueous copolymer dispersions comprise asmonomers of group a) N,N-dimethylaminopropyl(meth)acrylamide and/orN,N-dimethylaminoethyl(meth)acrylate, and as monomer of group b) stearyl(meth)acrylate.
 3. The paper sizing agents according to claim 1characterized by a content of a copolymer which, after polymerization,is neutralized with inorganic and/or organic acids, and emulsified withwater, the pH-value in the end product being in the range of 3.0-8.0,and the amino groups of the monomers of group a) optionally beingreacted with a quaternizing agent in the molar ratio of amino groups toquaternizing agents of 100:1 to 1:1.
 4. The paper sizing agentsaccording to claim 1 characterized by a content of a copolymerquaternized with epichlorohydrin in the molar ratio of amino groups toepichlorohydrin of 50:1 to 1:1.
 5. The paper sizing agents according toclaim 1 characterized by a solids content of 10-60%-wt. of polymer. 6.The paper sizing agents according to claim 5 characterized by a solidscontent of 20-50%-wt of polymer.
 7. The paper sizing agents according toclaim 6 characterized by a solids content of 30-40%-wt of polymer.
 8. Aprocess for the production of paper sized in the pulp by using acationic copolymer dispersion, characterized in that an aqueouscopolymer dispersion as defined in claim 1 is used as pulp sizing agent,which is mixed to the high-density or low-density pulp in an amount of0.1% to 3.0% of copolymer, relative to abs. dry pulp, under intensestirring, and that the sized paper is isolated and dried.
 9. A processfor the production of paper sized at the surface by using a cationiccopolymer dispersion, characterized in that an aqueous copolymerdispersion according to claim 1 is used as surface sizing agent, with0.1-5.0 g of copolymer per m² of paper being applied after the dryingsection.
 10. The paper sizing agents according to claim 2, characterizedin that the aqueous copolymer dispersions comprise as monomers of groupa) N,N-dimethylaminopropylacrylamide and/orN,N-dimethylaminoethylacrylate.
 11. The paper sizing agents according toclaim 3, wherein said inorganic and/or organic acids are carboxylicacids.